To ensure that textiles fulfill their purpose and have the desired properties in terms of feel, appearance and behaviour when in use, they are processed specifically. In addition to the extraction of fibers, the production of yarns and threads and formation of surface properties there are further methods which influence the textile properties.
Depending on the intended purpose it may be necessary for the textile to have greater stability, greater volume in the thread-like product or increased temperature resistance, to give but a few examples.
Many of these methods require subsequent thermal fixing which is usually performed using superheated steam under atmospheric pressure or pressurised saturated steam, in order to permanently stabilise the desired properties. Usually, the fixing process is referred to in the textile industry as heat setting, in the field of carpet yarn production the synonym heatset process is used.
In the field of carpet yarn production for example there are straight set yarns and frieze yarns. Whereas with a straight set yarn the straight linear structure of the single yarns or the cabled yarns or threads is heat set, in the case of frieze yarns after the cabling process the yarn is shaped three-dimensionally by bending/compressing and this state is then made permanent by thermal treatment. In addition, the thermal treatment causes a shrink billowing of the thread which increases the volume of the thread.
The term thread is defined in terms of this application to mean all linear forms. These can include yarns, threads but also film tapes and looped and ribbon-like textiles and the like. The term thread is used synonymously in all of the possible alternatives in this application for reasons of simplification.
German Patent Publication DE 39 38 183 A1 discloses a device for the continuous thermal treatment of yarns. To improve the sealing of the device at the inlet and outlet opening an inlet pre-zone is arranged upstream and an outlet pre-zone is arranged downstream. So-called yarn climate barriers are also integrated into the pre-zone which deflect the steam inside the device so that superheated steam is prevented from escaping. The counterflow principle is also intended to create a specific seal, so that no cold air can flow from the outside into the actual fixing chamber. In addition, in the region of the inlet opening narrow plates are also arranged which also make it more difficult for cold external air to enter.
In German Patent Publication DE 195 16 127 B4 a treatment chamber is also described for the continuous thermal treatment of yarns. In the area of the inlet and outlet opening so-called ventilation barriers are provided which are used for sealing the treatment chamber from the surrounding air. Here a counterflow is produced by means of fans which is guided vertically upwards and suctioned away.
By means of European Patent Publication EP 1 055 763 A2 a method and a device are known for continuously treatment a length of material with steam for fixing. Here before the inlet or outlet opening an inlet or outlet control is arranged with a suction device. Furthermore, by means of intermediate plates both controls are designed so that there is only a gap for the length of material and possibly a conveyor belt.
In US Published Patent Application 2009/0188772 A1 an additional, alternative machine is described for the thermal treatment of yarns. Said machine comprises a sealing head at the inlet and outlet opening, which comprises two rollers which press against opposite surfaces of the conveyor belt.
A further variant of a yarn finishing system is disclosed in European Patent Publication EP 2 221 404 A2. To prevent steam escaping from the treatment chamber the openings for transporting the yarn in and out are closed as far as possible by a steam barrier. Said steam barrier contains a rotatable roller which lies on the yarn lying on the conveyor belt, as well as a sheet metal screen which closes the opening as far as possible and so-called sealing lips which are arranged on the lower side of the tractive strand and on the upper and lower side of the loose strand. The roller can have different surface shapes and if necessary can be opened by a mechanism, in case of material blockage or for cleaning.
The disadvantage of devices which clamp the thread between one or two rollers and the conveyor belt has proved to be that at the points where the placed threads cross over one another, pressure points are created over the length of a yarn diameter which are also fixed. Said pressure points affect the uniformity of the yarn as in this area the compression is greater, which for example during dyeing and during later surface finishing results in an uneven product. In the final product of the textile surface said points are then slightly lighter because of their different light reflective behaviour. This occurs when threads are placed on a conveyor belt. According to the belt speed in practice the density is relatively high and several centimeters thick, so that the threads are frequently forced to cross over one another. The conveyor belt with the threads lying thereon runs through the gore of the squeezing roller pairs or the rollers on the conveyor belt, and this has a negative effect particularly at the outlet opening, through which the recently heated threads run through the output roller(s) into the cooler atmosphere. Mainly if the threads have not yet been cooled completely said deformations remain in permanent form and are fixed permanently during the subsequent cooling. Furthermore, it can cause the flattening of the threads.
Furthermore, with slit screens and differently designed narrow outlets there is a risk that the threads can accumulate at the upper edge. In particular, with a high density of threads and the associated high occupancy density there are displacements, accumulations and reorientations of the upper thread layers. This can lead to catching during the subsequent removal of the threads from the conveyor belt. Furthermore, the fiber materials can be damaged by friction on the sealing parts.
In addition, yarn climate barriers, ventilation barriers and the like are not only structurally expensive and increase the costs of a device for thermal treatment, but also the use/operation of such devices is expensive.